On Wednesday, Google plans to make it easier for users to access music online by integrating song preview and purchase links into its search index.

Users who enter music-related queries -- not only song names but partial song lyrics -- will be presented with a list of relevant songs from Google partners MySpace and LaLa. Clicking on a song in the search results list will play a song preview and provide a link to buy and download the song.

Google has also partnered with music streaming services Pandora, iMeem and Rhapsody to expose searchers to new music.

Geoff Ralston, CEO of Lala.com, says there's a shift going on in the music industry. His company's partnership with Google, he says, is "about getting consumers to the music they're looking for faster. What music is all about right now is discovery."

For the LaLa.com song links that Google presents, searchers will be able to preview songs in their entirety the first time, and then for 30 seconds on subsequent listens. Songs can be purchased using any of LaLa.com's accepted payment methods -- Visa, MasterCard, American Express, and PayPal -- or through Google Checkout.

Google's universal search effort, through which the company has integrated different media types like video into a single search index, appears to be evolving into something that might be described as Google commercial search.

According to Google, two of the top ten queries in the U.S. since 2004 are music-related.

For Apple and its iTunes Store -- which by NPD Group figures held a 69% share of the digital music download market in the first half of the year -- Google's entry into the music market presents a serious challenge.

Competitive tensions between the two companies have been rising recently. Earlier on Wednesday, Google introduced Google Maps Navigation, a free Internet-connected navigation service that competes with paid iPhone navigation apps. And on Tuesday, Google made Google Voice's voicemail system available with existing mobile phone numbers, a move that could displace AT&T's voicemail system on the iPhone.

Blue Cross of Northeast Pennsylvania, the University of Louisville School of Medicine, and a range of large and small healthcare providers are using mobile apps to improve care and help patients manage their health. Find out how. Download the report here (registration required).